FIGURE G.2 The velocity response of the Streckheisen STS-1 seismometer including the feedback poles and zeroes used to shape the spectrum as discussed in the text. SOURCE: Derived from a standard model of the STS-1 velocity response; with permission from Pete Davis, IRIS/IDA Project.

FIGURE G.2 The velocity response of the Streckheisen STS-1 seismometer including the feedback poles and zeroes used to shape the spectrum as discussed in the text. SOURCE: Derived from a standard model of the STS-1 velocity response; with permission from Pete Davis, IRIS/IDA Project.

The response of the GSN standard seismometer has been shaped to be nominally flat ato ground velocity between about 2.8 mHz and 5 Hz. For frequencies below 2.8 mHz, the seismometer’s output has been shaped so that at zero frequency its output is zero. In the W phase band (1-10 MHz) the response is critically dependent on the exact parameters of the seismometer’s feedback circuit.

In a very real sense, the GSN standard seismometer was not designed to support a simple deconvolution of velocity to displacement. Furthermore, many of the STS-1s in the GSN are now more than two decades old and, because the STS-1 is no longer manufactured, spares are not available. More details can be found at http://www.iris.edu/hq/gsn/quality, and a report “The IRIS/GSN Data Quality Initiative: Assessment of and proposed metrics for the GSN dataset” is in draft form. The USGS and the National Science Foundation (NSF) must seriously



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